JP7014552B2 - Viscosity index improver and lubricating oil composition - Google Patents

Description

The present invention relates to a viscosity index improver and a lubricating oil composition containing the same.

In recent years, there has been a strong demand for improving fuel efficiency of lubricating oils for internal combustion engines, and one means is to reduce friction loss by reducing the viscosity of the lubricating oils. However, simply lowering the viscosity causes problems such as liquid leakage and seizure, so it is effective to add a viscosity index improver having an effect of keeping the viscosity at a low temperature low while keeping the viscosity at a high temperature high.

Viscosity index improvers are known to contain a polymer, and there are various types. Among them, the viscosity index improver made of an alkyl (meth) acrylate polymer exhibits a high viscosity index improving effect. On the other hand, the viscosity index improver made of an alkyl (meth) acrylate polymer has a problem that the fuel efficiency property is deteriorated (poor long life property) during long-term use because the shear stability is poor.

As a means for improving the shear stability, for example, reducing the molecular weight of the polymer contained in the viscosity index improver can be mentioned. In general, the lower the molecular weight of a polymer, the less susceptible it is to shearing, and the smaller the amount of decrease in molecular weight. Therefore, by using a low molecular weight polymer as a viscosity index improver, it is possible to suppress the decrease in viscosity after shearing. Yes (Patent Document 1 and Non-Patent Document 1). In addition, there are reports of attempts to improve shear stability by using a polymer having a star-shaped structure using divinylbenzene in the core portion (Patent Document 2), and reports of using a comb-shaped polymer as a component of a lubricating oil composition. (Patent Documents 3 and 4).

Japanese Unexamined Patent Publication No. 2013-104032 Japanese Unexamined Patent Publication No. 2012-197399 Special Table 2010-532805 Gazette Special Table 2012-520358 Gazette

Nakata, "Viscosity Index Improver for High Performance Engine Oil", Sanyo Kasei News, Sanyo Kasei Kogyo Co., Ltd., 2013, No. 476

However, in general, the lower the molecular weight of the polymer, the lower the effect of improving the viscosity index tends to be. Therefore, when a polymer having a low molecular weight is used as the viscosity index improving agent, there arises a problem that the viscosity index becomes low. Further, in order to adjust the viscosity to a desired value, it is necessary to increase the amount of the viscosity index improver used, which tends to be disadvantageous in terms of cost. Further, the lubricating oil composition includes a lubricating oil base oil, various additives, a viscosity index improver and the like, and among them, the viscosity index improver is generally treated as a base oil composition dissolved in the base oil. When the concentration of the viscosity index improver in the base oil composition is high, not only the degree of freedom of formulation in the lubricating oil composition is increased, but also the amount of the lubricating oil base oil used per unit mass in the viscosity index improver is increased. Although it is advantageous in terms of cost such as manufacturing and transportation, the viscosity of the base oil composition increases and it becomes difficult to handle it at around room temperature. In some cases, equipment was required and productivity decreased.

The present invention has been made in view of the above problems, and an object thereof is to have a high viscosity index and good shear stability, and when a base oil solution is used, it has high fluidity near room temperature and is easy to handle. It is an object of the present invention to provide a viscosity index improver and a lubricating oil composition using the viscosity index improver.

The viscosity index improver of the present invention that has been able to solve the above problems has a unit (A) derived from a macromonomer and an alkyl (meth) acrylate derived from the alkyl group having 2 to 6 carbon atoms. A viscosity index improver containing a polymer having a unit (B), wherein the content of the unit (A) is 6 parts by mass or more and less than 20 parts by mass, and the unit (B) is contained in 100 parts by mass of the polymer. The amount is 40 parts by mass or more and less than 74 parts by mass, the total content of the unit (A) and the unit (B) is 46 parts by mass or more and less than 80 parts by mass, and the viscosity measured by the following method is 25 Pa · s or less. However, it has a feature.
(Viscosity measurement)
A solution consisting of 80% by mass of Group III base oil (viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² / s) and 20% by mass of the polymer in the American Petroleum Institute (API) classification is used in a viscometer (Toki Sangyo). Measured at 25 ° C with TVE-35H, 3 ° x R9.7 rotor) manufactured by the company.

The viscosity index improver of the present invention preferably further has a unit (C) in which the polymer is derived from an alkyl (meth) acrylate and the alkyl group has 11 to 40 carbon atoms, and the unit (C). The content of is preferably 3 parts by mass or more and 40 parts by mass or less in 100 parts by mass of the polymer. The polymer may further have a unit (D) derived from a maleimide-based monomer, and the content of the unit (D) is 1 part by mass or more and 20 parts by mass or less in 100 parts by mass of the polymer. Is preferable. The content of the unit derived from the styrene-based monomer is preferably less than 3 parts by mass in 100 parts by mass of the polymer. The unit (A) of the polymer preferably has a repeating structure of branched chain alkylene groups.

The present invention also provides a lubricating oil composition containing a lubricating oil base oil and the above-mentioned viscosity index improver.

By using the viscosity index improver of the present invention, it is possible to exhibit a high viscosity index and good shear stability when used as a base oil solution. Further, since the base oil solution of the viscosity index improver of the present invention has high fluidity near room temperature and is easy to handle, workability and productivity when preparing a lubricating oil composition are improved.

The 1H-nuclear magnetic resonance (NMR) spectrum of the macromonomer ¹ produced in Production Example 1 is represented. ^The 1H-nuclear magnetic resonance (NMR) spectrum of the macromonomer 2 produced in Production Example 2 is represented.

[1. Viscosity index improver]
The viscosity index improver of the present invention comprises a polymer having a unit (A) derived from a macromonomer and a unit (B) derived from an alkyl (meth) acrylate and having 2 to 6 carbon atoms in the alkyl group. It contains. The viscosity index improver of the present invention contains a polymer having a unit (A) and a unit (B) in a predetermined ratio, so that it has excellent solubility in a base oil and is used as a base oil solution. Sometimes it shows a high viscosity index and can also improve shear stability. Therefore, if the viscosity index improver of the present invention is used, both the viscosity index and the shear stability, which are contradictory to each other in relation to the molecular weight of the polymer, can be improved. Further, the viscosity index improver of the present invention has high fluidity and excellent handleability when used as a base oil solution.

The unit (A) derived from the macromonomer is a structural unit that can be introduced into the polymer by polymerizing the macromonomer. As the macromonomer, any polymer having a polymerizable functional group can be used without particular limitation, but one having a repeating structure derived from a hydrocarbon monomer is used from the viewpoint of enhancing the solubility of the polymer in the base oil. preferable. Examples of the hydrocarbon monomer include monoolefins such as ethylene, propylene, 1-butene, isobutene, 1-tetradecene and 1-octadecene; 1,3-butadiene, 2-methyl-1,3-butadiene, 1, Alkenes such as 3-pentadiene, 1,4-pentadiene, 1,5-hexadiene, 2,5-dimethyl-1,5-hexadiene (also known as diisobutene); styrene-based monomers such as styrene, α-methylstyrene and vinyltoluene. Quantum and the like can be mentioned. It is preferable that the alkazienes complete the polymerization reaction with one ethylenic carbon-carbon double bond left, and the unreacted ethylenic carbon-carbon double bond portion is hydrogenated after the polymerization. Is preferable. As the hydrocarbon monomer, monoolefins, alkenes and the like are preferable, and the carbon number of these monoolefins and alkenes is preferably about 2 to 20 and more preferably about 2 to 10. It is more preferably about 3 to 6.

As the unit (A) derived from the macromonomer, the polymer according to the present invention can be obtained by copolymerizing the macromonomer with the monomer forming the unit (B) and the like, and the macromonomer can be easily produced and obtained. Since it is easy to obtain, the one represented by the following formula (1) is preferable. In the following formula (1), R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X ¹ is a single bond, an alkylene group, -O-, -CO-, -NH- or a combination thereof. The group represents a group, and R ² represents the polymer structural part of the macromonomer.

Examples of the alkyl group having 1 to 4 carbon atoms of R ¹ in the formula (1) include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group and the like. The number of carbon atoms of the alkyl group of R ¹ is more preferably 1 to 3, and even more preferably 1 to 2. Among them, R ¹ is preferably a hydrogen atom or a methyl group.

When X ¹ of the formula (1) is a single bond, the polymer structural part of R ² is directly bonded to the ester group of the formula (1), and X ¹ of the formula (1) is a linking group such as an alkylene group. In the case, the polymer structure portion of R ² is bonded to the ester group of the formula (1) via a linking group. When the linking group of X ¹ contains an alkylene group, the alkylene group is preferably linear or branched, preferably 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, and 1 to 3 carbon atoms. Is even more preferable. The linking group of X ¹ also includes an ester bond (-CO-O-), an amide bond (-CO-NH-), a urethane bond (-NH-CO-O-), and the like, in addition to those containing an alkylene group. The X ¹ contains one or more selected from these bonds because the viscosity of the base oil solution of the viscosity index improver decreases near room temperature and the handleability is improved. preferable.

The polymer structural portion of R ² of the formula (1) preferably contains a repeating structure derived from a hydrocarbon monomer, and examples of the hydrocarbon monomer include those exemplified above. The polymer structure is preferably a polymer of monoolefins and / or alkazienes, and if an unsaturated bond remains after the polymerization, it is more preferable that the unsaturated bond is hydrogenated. Since such a preferable polymer structure portion is formed of carbon and hydrogen as a whole, it is referred to as a macrohydrocarbon group in the present specification. Similarly, when it does not contain an unsaturated bond, it is referred to as a macroalkyl group.

The macrohydrocarbon group or the macroalkyl group may be linear or branched, but when used as a viscosity index improver, it suppresses crystallization at low temperatures and prevents thickening. From the point of view, it is preferably in the form of a branched chain. The branched macrohydrocarbon group or macroalkyl group preferably contains a branched alkylene group as a repeating unit, and contains both a branched alkylene group and a linear alkylene group as a repeating unit. Is preferable. Examples of the branched alkylene group include a 1,2-propylene group, a 1,2-butylene group, a 1,3-butylene group, a 2,3-butylene group and a 1,2-hexylene group. Examples of the linear alkylene group include ethylene, 1,3-propylene group, 1,4-butylene group, 1,5-pentylene group, 1,6-hexylene group and the like.

The polymer may contain only one type of the unit (A) derived from the macromonomer, or may contain two or more types.

The molecular weight of the unit (A) derived from the macromonomer is preferably 500 or more, more preferably 1000 or more, still more preferably 1500 or more, still more preferably 2000 or more, from the viewpoints of base oil solubility, viscosity index, and shear stability. Further, 50,000 or less is preferable, 20,000 or less is more preferable, and 10,000 or less is further preferable. In the unit represented by the above formula (1), the number of carbon atoms of the macrohydrocarbon group or macroalkyl group of R ² is preferably 35 or more, more preferably 50 or more, further preferably 70 or more, and 100 or more. Is even more preferable, and 3500 or less is preferable, 1500 or less is more preferable, and 700 or less is further preferable.

The content of the unit (A) in the polymer is 6 parts by mass or more and less than 20 parts by mass in 100 parts by mass of the polymer. The polymer contains a unit (B), which will be described later. However, the polymer contains the unit (A) because the solubility in the base oil tends to decrease due to the inclusion of the unit (B). If it is contained in such a content, the solubility of the viscosity index improver in the base oil can be enhanced. Further, in combination with the inclusion of the unit (B) in the polymer, the viscosity index of the base oil solution of the viscosity index improver can be improved, and the shear stability of the viscosity index improver can be improved. The content of the unit (A) in the polymer is preferably 7 parts by mass or more, more preferably 8 parts by mass or more, preferably 18 parts by mass or less, and more preferably 16 parts by mass or less in 100 parts by mass of the polymer. ..

The unit (B) is a unit derived from an alkyl (meth) acrylate and having 2 to 6 carbon atoms of the alkyl group. The unit (B) can be introduced into a polymer by copolymerizing an alkyl (meth) acrylate having an alkyl group having 2 to 6 carbon atoms with the macromonomer or the like described above.

The unit (B) is preferably a unit represented by the following formula (2). In formula (2), R ³ represents a hydrogen atom or a methyl group, and R ⁴ represents an alkyl group having 2 to 6 carbon atoms.

The alkyl group having 2 to 6 carbon atoms of R ⁴ in the formula (2) is a straight chain such as an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a pentyl group and a hexyl group. Examples thereof include a cyclic or branched alkyl group and a cyclic alkyl group such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group and a cyclohexyl group. The alkyl group of R ⁴ is preferably linear or cyclic, more preferably linear. The number of carbon atoms of the alkyl group of R ⁴ is preferably 3 to 5 if it is linear or branched, and 5 to 6 if it is cyclic. Among them, the alkyl group of R ⁴ is a butyl group or a cyclohexyl group because of the availability of the alkyl (meth) acrylate giving the unit (B) and the excellent fluidity of the viscosity index improver near room temperature. Is preferable, and an n-butyl group or an isobutyl group is more preferable.

The polymer may contain only one type of unit (B) derived from an alkyl (meth) acrylate having an alkyl group having 2 to 6 carbon atoms, or may contain two or more types.

The content of the unit (B) in the polymer is usually 40 parts by mass or more, preferably 45 parts by mass or more, more preferably 50 parts by mass or more, still more preferably 55 parts by mass or more in 100 parts by mass of the polymer. .. If the unit (B) is contained in such a content, the base of the viscosity index improver is compared with the case where a unit derived from methyl (meth) acrylate is introduced into the polymer instead of the unit (B), for example. The viscosity of the oil solution near room temperature is reduced, and the handleability can be improved. In addition, the viscosity index of the base oil solution of the viscosity index improver is improved, and the shear stability of the viscosity index improver is also improved. On the other hand, the content of the unit (B) in the polymer is usually less than 74 parts by mass, preferably 72 parts by mass or less, more preferably 70 parts by mass or less, and 68 parts by mass or less in 100 parts by mass of the polymer. More preferred. If the unit (B) is contained in such a content, the solubility of the viscosity index improver in the base oil can be enhanced.

The total content of the unit (A) and the unit (B) is 100 parts by mass from the viewpoint of increasing the viscosity index of the base oil solution of the viscosity index improver and increasing the shear stability of the viscosity index improver. Of these, it is usually 46 parts by mass or more, preferably 50 parts by mass or more, more preferably 53 parts by mass or more, further preferably 56 parts by mass or more, still more preferably 60 parts by mass or more. Further, from the viewpoint of enhancing the solubility of the viscosity index improver in the base oil, the total content of the unit (A) and the unit (B) is usually less than 80 parts by mass and 79 parts by mass or less in 100 parts by mass of the polymer. Is preferable.

The polymer contained in the viscosity index improver is further preferably derived from an alkyl (meth) acrylate and has a unit (C) in which the alkyl group has 11 to 40 carbon atoms. When the unit (C) is contained in the polymer, it becomes easy to increase the solubility of the viscosity index improver in the base oil. The unit (C) is heavy by copolymerizing an alkyl (meth) acrylate having an alkyl group having 11 to 40 carbon atoms with the macromonomer described above, an alkyl (meth) acrylate giving the unit (B), or the like. Can be introduced into coalescence.

The unit (C) is preferably a unit represented by the following formula (3). In formula (3), R ⁵ represents a hydrogen atom or a methyl group, and R ⁶ represents an alkyl group having 11 to 40 carbon atoms.

Examples of the alkyl group having 11 to 40 carbon atoms of R ⁶ in the formula (3) include an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group and a tetracosyl. A linear or branched alkyl group such as a group or a 2-decyltetradecyl group, or a cyclic alkyl group such as a cycloheptyl group, a cyclooctyl group, a cyclononyl group, a cyclodecyl group, a dicyclopentanyl group or an adamantyl group. And so on. The alkyl group of R ⁶ is preferably linear or branched chain, more preferably linear. The number of carbon atoms thereof is preferably 12 or more, more preferably 14 or more, more preferably 35 or less, and even more preferably 30 or less.

The polymer may contain only one type of unit (C) derived from an alkyl (meth) acrylate having an alkyl group having 11 to 40 carbon atoms, or may contain two or more types.

The content of the unit (C) in the polymer may be 0 parts by mass or more in 100 parts by mass of the polymer. When the polymer contains the unit (C), the content thereof is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, further preferably 10 parts by mass or more, and 40 parts by mass in 100 parts by mass of the polymer. It is preferably parts or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less. If the unit (C) is contained in the polymer at such a content, it becomes easy to increase the solubility of the viscosity index improver in the base oil.

When the polymer has a unit (C) in addition to the unit (A) and the unit (B), the total content of the unit (A), the unit (B) and the unit (C) in the polymer is 100. Of the parts by mass, 49 parts by mass or more is preferable, 60 parts by mass or more is more preferable, 70 parts by mass or more is further preferable, and 80 parts by mass or more is even more preferable. The upper limit of the total content of the unit (A), the unit (B) and the unit (C) in the polymer is not particularly limited, and the polymer is substantially composed of the unit (A), the unit (B) and the unit (C). The total content of the unit (A), the unit (B) and the unit (C) in the polymer may be 98 parts by mass or less in 100 parts by mass of the polymer. It may be 95 parts by mass or less.

The polymer contained in the viscosity index improver may have a unit (D) derived from a maleimide-based monomer. In this case, the succinimide ring structure is introduced into the main chain of the polymer, which is derived from the maleimide-based monomer. By introducing the ring structure into the main chain of the polymer in this way, it is possible to improve the shear stability and heat resistance of the viscosity index improver while ensuring the solubility of the viscosity index improver in the base oil. .. Further, when it is used as a lubricating oil composition, it is expected to have effects such as improvement of clean dispersibility of sludge and the like and suppression of wear on the metal surface. The unit (D) is a polymer obtained by copolymerizing maleimide, which may have a substituent at the N-position, with the macromonomer described above, the alkyl (meth) acrylate giving the unit (B), or the like. Can be introduced.

The unit (D) is preferably a unit represented by the following formula (4). In formula (4), R ⁷ and R ⁸ independently represent a hydrogen atom or an alkyl group, and R ⁹ represents a hydrogen atom or an organic group having 1 to 40 carbon atoms.

The alkyl group of R ⁷ and R ⁸ of the formula (4) preferably has 1 to 8 carbon atoms, more preferably 1 to 4 carbon atoms, and even more preferably 1 to 3 carbon atoms. As R ⁷ and R ⁸ , a hydrogen atom, a methyl group or an ethyl group is more preferable, and a hydrogen atom or a methyl group is further preferable.

Examples of the organic group of R ⁹ in the formula (4) include an alkyl group, an aryl group, an aralkyl group, a group in which a part of —CH ₂ − contained in the alkyl group is replaced with —O—, and the like. Substituents such as a hydroxyl group, a halogen group, a nitro group, an alkyl group (in the case of an aryl group and an aralkyl group), an alkoxy group and a carboxy group may be bonded to the group. The organic group of R ⁹ is preferably 1 to 24 carbon atoms, more preferably 1 to 18 carbon atoms, and even more preferably 1 to 12 carbon atoms, from the viewpoint of increasing the solubility of the viscosity index improver in the base oil.

The alkyl group of R ⁹ includes methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group, isopentyl group, n-hexyl group and iso. Linear or branched alkyl groups such as xyl group, n-heptyl group, isoheptyl group, n-octyl group, 2-ethylhexyl group, cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cyclononyl group, Examples thereof include a cyclic alkyl group such as a cyclodecyl group, a dicyclopentanyl group and an adamantyl group. Examples of the aryl group of R ⁹ include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a biphenyl group and the like. Examples of the aralkyl group of R ⁹ include a benzyl group and a naphthylmethyl group. Examples of the group in which a part of —CH ₂ − contained in the alkyl group of R ⁹ is replaced with —O— include a polyoxyalkylene group such as a polyoxyethylene group and a polyoxypropylene group. It should be noted that R ⁹ is preferably an aryl group from the viewpoint that it is easy to improve the shear stability of the viscosity index improver, and R ⁹ is cycloalkyl from the viewpoint that it is easy to improve the viscosity index. It is preferably a group.

Specific examples of maleimide-based monomers include maleimide, N-methylmaleimide, N-isopropylmaleimide, N-butylmaleimide, N-isobutylmaleimide, Nt-butylmaleimide, N-cyclohexylmaleimide, and N-octyl. Maleimide, N-2-ethylhexylmaleimide, N-decylmaleimide, N-laurylmaleimide, N-tetradecylmaleimide, N-stearylmaleimide, N-2-decyltetradecylmaleimide, N-phenylmaleimide, N-benzylmaleimide, N -Chlorophenylmaleimide, N-methylphenylmaleimide, N-naphthylmaleimide, N-hydroxylethylmaleimide, N-hydroxylphenylmaleimide, N-methoxyphenylmaleimide, N-carboxyphenylmaleimide, N-nitrophenylmaleimide, N-tribromophenyl Maleimide and the like can be mentioned. Among these, N-phenylmaleimide and N-cyclohexylmaleimide are examples of maleimide-based monomers because they are easily available and the solubility of the viscosity index improver in the base oil can be easily improved. , N-Isopropylmaleimide, N-benzylmaleimide, N-laurylmaleimide, N-stearylmaleimide are preferred. Among them, N-phenylmaleimide is preferable as the maleimide-based monomer from the viewpoint of improving the shear stability of the viscosity index improver, and N-cyclohexylmaleimide is preferable from the viewpoint of improving the viscosity index.

The polymer may contain only one type of the unit (D) derived from the maleimide-based monomer, or may contain two or more types.

The content of the unit (D) in the polymer may be 0 parts by mass or more in 100 parts by mass of the polymer. When the polymer contains the unit (D), the content thereof is preferably 1 part by mass or more, more preferably 2 parts by mass or more, further preferably 3 parts by mass or more, and 20 parts by mass in 100 parts by mass of the polymer. It is preferably 10 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less. This makes it easier for the effect of including the unit (D) in the polymer to be effective.

The polymer contained in the viscosity index improver may have a unit derived from a monomer other than the units (A) to (D) described above (hereinafter, referred to as “unit (E)”). .. The units (A) to (D) can be introduced as a constituent unit of the polymer by radically copolymerizing the corresponding macromonomers, alkyl (meth) acrylates, and maleimide-based monomers, respectively, and thus the units ( E) is also preferably a unit derived from a radically polymerizable monomer. The radically polymerizable monomer forming the unit (E) includes a monofunctional monomer having one radically polymerizable group in the molecule and a polyfunctional single amount having two or more radically polymerizable groups in the molecule. It can be classified as a body.

Examples of monofunctional monomers include (meth) acrylates other than alkyl (meth) acrylates forming the unit (B) and unit (C), unsaturated mono or dicarboxylic acid esters, unsaturated carboxylic acids, and vinyl aromatics. Examples thereof include compounds, vinyl esters, vinyl ethers, olefins, vinyl cyanide, N-vinyl compounds and the like. The unit (E) formed from these monofunctional monomers may be only one kind or two or more kinds.

Examples of the (meth) acrylate other than the alkyl (meth) acrylate forming the unit (B) and the unit (C) include methyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and 2-hydroxyethyl. (Meta) acrylate, 2-hydroxybutyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, morpholinoalkylene (meth) acrylate , Α-Hydroxymethyl acrylate methyl, polyethylene glycol mono (meth) acrylate and the like.

Examples of unsaturated mono or dicarboxylic acid esters include butyl phthalate, octyl crotonate, dibutyl maleate, dilauryl maleate, dioctyl fumarate, distearyl fumarate and the like.
Examples of unsaturated carboxylic acids include (meth) acrylic acid, maleic acid, fumaric acid, maleic anhydride and the like.
Examples of the vinyl aromatic compound include styrene-based monomers such as styrene, α-methylstyrene, vinyltoluene and methoxystyrene, 2-vinylpyridine, 4-vinylpyridine and the like.
Examples of the vinyl ester include vinyl acetate, vinyl propionate, vinyl octylate and the like.
Examples of the vinyl ether include methyl vinyl ether, butyl vinyl ether, octyl vinyl ether, dodecyl vinyl ether and the like.
Examples of the olefins include ethylene, propylene, 1-butene, isobutene, 1-tetradecene, 1-octadecene, diisobutene and the like.
Examples of vinyl cyanide include acrylonitrile and methacrylonitrile.
Examples of the N-vinyl compound include N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylimidazole, N-vinylmorpholine, N-vinylacetamide and the like.

Among these monofunctional monomers, the unit (E) is preferably a (meth) acrylate or N-vinyl compound other than the alkyl (meth) acrylate forming the unit (B) or the unit (C), preferably 2-. Hydroxyethyl (meth) acrylates, N, N-dimethylaminoethyl (meth) acrylates, methyl α-hydroxymethylacrylate, and N-vinylpyrrolidone are particularly preferred.

Examples of the polyfunctional monomer forming the unit (E) are polyfunctional (meth) acrylate, vinyl ether group-containing (meth) acrylate, allyl group-containing (meth) acrylate, and polyfunctional (meth) acryloyl group-containing isocyanurate. , Polyfunctional (meth) acrylic compounds such as polyfunctional urethane (meth) acrylates, polyfunctional maleimide-based compounds, polyfunctional vinyl ethers, polyfunctional allyl-based compounds, polyfunctional aromatic vinyl and the like. The unit (E) formed from these polyfunctional monomers may be only one kind or two or more kinds.

Examples of the polyfunctional (meth) acrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, hexanediol di (meth) acrylate, and bisphenol A alkylene oxide di (meth). Examples thereof include acrylate, trimethylolpropane tri (meth) acrylate, 2,2'-[oxybis (methylene)] bisacrylic acid, dialkyl-2,2'-[oxybis (methylene)] bis-2-propenoate.

Examples of the vinyl ether group-containing (meth) acrylate include 2-vinyloxyethyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, and 2- (vinyloxyethoxy) ethyl (meth) acrylate.
Examples of the allyl group-containing (meth) acrylate include allyl (meth) acrylate, methyl α-allyloxymethylacrylate, stearyl α-allyloxymethylacrylate, 2-decyltetradecylate α-allyloxymethylacrylate, and the like. Can be mentioned.
Examples of the polyfunctional (meth) acryloyl group-containing isocyanate include tri (acryloyloxyethyl) isocyanurate and tri (methacryloyloxyethyl) isocyanurate.
Examples of the polyfunctional urethane (meth) acrylate include polyfunctional isocyanates such as tolylene diisocyanate, isophorone diisocyanate, and xylylene diisocyanate, and hydroxyl groups such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate. Examples thereof include polyfunctional urethane (meth) acrylate obtained by reaction with the contained (meth) acrylic acid ester.

Examples of the polyfunctional maleimide-based compound include 4,4'-diphenylmethane bismaleimide, m-phenylene bismaleimide, bisphenol A diphenyl ether bismaleimide, and 1,6-bismaleimide- (2,2,4-trimethyl) hexane. Can be mentioned.
Examples of the polyfunctional vinyl ether include ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, hexanediol divinyl ether, bisphenol A alkylene oxide divinyl ether, and trimethylolpropane trivinyl ether.
Examples of the polyfunctional allyl compound include ethylene glycol diallyl ether, diethylene glycol diallyl ether, polyethylene glycol diallyl ether, hexanediol diallyl ether, bisphenol A alkylene oxide diallyl ether, trimethylolpropanetriallyl ether, and ditrimethylolpropanetetraallyl ether. Polyfunctional allyl ether; polyfunctional allyl group-containing isocyanurate such as triallyl isocyanurate; polyfunctional allyl ester such as diallyl phthalate and diallyl diphenate; bisallyl nadiimide compound and the like; bisallyl nadiimide compound and the like. ..
Examples of the polyfunctional aromatic vinyl include divinylbenzene and the like.

The content of the unit (E) in the polymer may be 0 parts by mass or more in 100 parts by mass of the polymer. When the polymer contains the unit (E), the content thereof is preferably 1 part by mass or more, more preferably 2 parts by mass or more, further preferably 3 parts by mass or more, and 50 parts by mass, based on 100 parts by mass of the polymer. It is preferably 40 parts by mass or less, more preferably 40 parts by mass or less, further preferably 30 parts by mass or less, further preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less.

It is preferable that the polymer does not contain many units derived from the styrene-based monomer. This is because when the content of the unit derived from the styrene-based monomer increases, the solubility of the viscosity index improver in the base oil tends to decrease, and the viscosity index tends to decrease. Therefore, the content of the unit derived from the styrene-based monomer is preferably less than 3 parts by mass, more preferably 2 parts by mass or less, and further preferably 1 part by mass or less in 100 parts by mass of the polymer. The styrene-based monomer includes not only styrene but also those in which a substituent is bonded to a benzene ring or a vinyl group of styrene, and examples thereof include styrene, α-methylstyrene, vinyltoluene and methoxystyrene.

Further, since vinyl ethers, olefins and the like have low radical copolymerizability with (meth) acrylate, it is preferable that the polymer does not contain many units derived from these from the viewpoint of ease of producing the polymer. For example, the total content of the unit (E) derived from these monomers is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less with respect to 100 parts by mass of the polymer.

The content of the unit (E) derived from the polyfunctional monomer in the polymer is preferably 0 parts by mass or more and 5 parts by mass or less, more preferably 3 parts by mass or less, and 2 parts by mass or less in 100 parts by mass of the polymer. Is even more preferable. If the content of the unit derived from the polyfunctional monomer exceeds the above range, gelation may proceed during polymerization, or the solubility of the viscosity index improver containing the polymer in the base oil may decrease. be.

However, 2,2'-[oxybis (methylene)] bisacrylic acid, dialkyl-2,2'-[oxybis (methylene)] bis-2-propenoate, α-allyloxymethylacrylate methyl, α-allyloxymethyl In the case of a polyfunctional monomer in which polymerization proceeds while cyclizing, such as stearyl acrylate and 2-decyltetradecyl oxymethylacrylate, the unit derived from the polyfunctional monomer in the polymer. The content may be 0 parts by mass or more and 30 parts by mass or less, 20 parts by mass or less, or 15 parts by mass or less with respect to 100 parts by mass of the polymer. In this case, due to the effect of the ring structure introduced into the main chain, the heat resistance of the viscosity index improver can be improved and the shear stability can be improved.

The polymer contained in the viscosity index improver may have a branching unit derived from a polyfunctional chain transfer agent or a polyfunctional polymerization initiator. If the polymer has such a branching unit, the shear stability of the viscosity index improver can be improved without significantly impairing the solubility of the viscosity index improver in the base oil.

As the polyfunctional chain transfer agent, it is preferable to use a trifunctional or higher functional mercaptan, and when the monomer component is radically copolymerized using such a chain transfer agent, the branch represented by the following formula (5) is formed. The unit (chain transfer agent residue) is introduced into the polymer. In the following formula (5), L ¹ represents an organic residue having an m valence, and m represents a number of 0 or more. m is preferably 0 to 5.

Examples of the trifunctional or higher polyvalent mercaptan include trimethylolpropanetrimercaptoacetate, trimethylolpropanetri (3-mercaptopropionate), pentaerythritol tetrakis mercaptoacetate, and pentaerythritol tetrakis (3-mercaptopropionate). Dipentaerythritol hexakis mercaptoacetate, dipentaerythritol hexakis (3-mercaptopropionate) and other compounds having three or more hydroxyl groups, carboxyl group-containing mercaptans polyester compounds, triazine polyvalent thiols, polyvalent epoxy compounds A compound in which hydrogen sulfide is added to a plurality of epoxy groups to introduce three or more mercapto groups per molecule, and three carboxyl groups of a polyvalent carboxylic acid and mercaptoethanol are esterified to form three per molecule. Examples thereof include compounds having the above mercapto groups. The polymer may contain only one type of branching unit derived from a trifunctional or higher functional chain transfer agent, or may contain two or more types.

It is preferable to use a trifunctional or higher functional peroxide as the polyfunctional polymerization initiator, and when such a polyfunctional polymerization initiator is used as a radical polymerization initiator, a branching unit represented by the following formula (6) (initiation). Agent residue) is introduced into the polymer. In the following formula (6), L ² represents an n-valent organic residue, and n represents a number of 0 or more. n is preferably 0 to 5.

Examples of the trifunctional or higher functional initiator include 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, tris (t-butylperoxy) triazine, 3,3', 4,4. Examples thereof include trifunctional or higher functional organic peroxides such as'-tetra (t-butylperoxycarbonyl) benzophenone. The polymer may contain only one type of branching unit derived from a trifunctional or higher functional initiator, or may contain two or more types.

The content (total content) of the branching unit derived from the polyfunctional chain transfer agent and / or the polyfunctional initiator in the polymer may be 0 parts by mass or more in 100 parts by mass of the polymer, and is 0.01 mass by mass. More than parts are preferable, 0.02 parts by mass or more are more preferable, 0.05 parts by mass or more are further preferable, 3 parts by mass or less are preferable, 2 parts by mass or less are more preferable, and 1 part by mass or less is further preferable. By setting the content of the branching unit in such a range, the molecular weight distribution of the polymer is narrowed and the shear stability can be improved. The polymer may not contain branching units derived from the polyfunctional chain transfer agent and / or the polyfunctional initiator.

The polymer contained in the viscosity index improver of the present invention is 80% by mass of Group III base oil (viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² / s) according to the American Petroleum Association (API) classification, and the polymer. The viscosity of a solution consisting of 20% by mass is 25 Pa · s or less when measured at 25 ° C. with a viscometer (TVE-35H, manufactured by Toki Sangyo Co., Ltd., 3 ° × R9.7 rotor). When the base oil solution of the polymer has such a viscosity, the fluidity of the viscosity index improver near room temperature is increased, and the handleability is improved. The viscosity is preferably 20 Pa · s or less, and more preferably 15 Pa · s or less. The lower limit of the viscosity is not particularly limited, and may be, for example, 0.1 Pa · s or more. As the Group III base oil having a viscosity index of 122 and a kinematic viscosity of 40 ° C. of 19.6 mm ² / s, YUBASE4 manufactured by SK Co., Ltd. is used. Further, the viscosity is measured by setting the rotation speed of the rotor to 50 rpm.

The viscosity index improver may contain a part of the raw material for producing the polymer together with the polymer as long as the performance is not significantly impaired. For example, the polymer obtained by the polymerization reaction is particularly purified. In the case of producing a viscosity index improver without using or highly purifying, the polymer raw material (for example, a monomer component, a polymerization initiator, a chain transfer agent, etc.) is contained in the viscosity index improver. It can be. In such a case, the polymer concentration of the base oil solution of the polymer used in the above viscosity measurement can be regarded as the polymer concentration including the polymer raw material in addition to the polymer. That is, a solution consisting of a total of 20% by mass of the polymer and the polymer raw material and 80% by mass of the group III base oil may be used for viscosity measurement. For example, the polymer concentration including the polymer raw material can also be determined by measuring the content of the base oil in the sample using gel permeation chromatography.

The polymer contained in the viscosity index improver preferably has a weight average molecular weight (Mw) of 100,000 or more, more preferably 200,000 or more, further preferably 300,000 or more, still more preferably 350,000 or more, and further. 700,000 or less is preferable, 650,000 or less is more preferable, and 600,000 or less is further preferable. When the weight average molecular weight of the polymer is small, the viscosity index of the base oil solution of the viscosity index improver tends to decrease, so that the amount of the viscosity index improver used to adjust the desired viscosity increases, which is cost effective. It will be disadvantageous. When the weight average molecular weight of the polymer is excessively large, the solubility of the viscosity index improver in the base oil tends to decrease, and the shear stability of the viscosity index improver tends to decrease.

The number average molecular weight (Mn) of the polymer contained in the viscosity index improver is preferably 90,000 or more, more preferably 110,000 or more, preferably 300,000 or less, and more preferably 250,000 or less.

The molecular weight distribution (Mw / Mn) calculated from Mw and Mn of the polymer is preferably 4.0 or less, more preferably 3.5 or less, still more preferably 3.0 or less. When the molecular weight distribution exceeds 4.0, the solubility of the viscosity index improver in the base oil becomes insufficient, and the shear stability of the lubricating oil composition tends to decrease. On the other hand, the lower limit of the molecular weight distribution is preferably 1.0, but the molecular weight distribution (Mw / Mn) is preferably 1.5 or more, more preferably 1.8 or more, from the viewpoint of easy synthesis of the polymer. The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polymer are determined by the methods described in Examples.

As a method for controlling the molecular weight, a known method can be used. For example, it can be controlled by adjusting the amount and type of the polymerization initiator / catalyst, the polymerization temperature, and the type and amount of the chain transfer agent. Living Radical Polymerization can also be used as a method for controlling the molecular weight distribution. As a specific method, the RAFT method, the NMP method, the ATRP method and the like are famous. For more information, see Aldrich Material Matters, Vol. 5, No. It is outlined in 1,2010. As an example of use, for example, in the case of the RAFT method, 2,2'-azobisisobutyronitrile is used as a polymerization initiator and dithiobenzoic acid cumil is used as a polymerization catalyst in Japanese Patent Application Laid-Open No. 2012-197399.

The glass transition temperature (Tg) of the polymer contained in the viscosity index improver is preferably −50 ° C. or higher, more preferably −40 ° C. or higher, further preferably −30 ° C. or higher, and preferably 0 ° C. or lower, −10 ° C. ° C. or lower is more preferable, and −20 ° C. or lower is even more preferable. When the Tg of the polymer is in such a range, the solubility in the base oil is ensured when the viscosity index improver is used as the base oil solution, and the fluidity near room temperature is maintained while maintaining the high viscosity index. It becomes easy to increase.

The SP value (solubility parameter) of the polymer contained in the viscosity index improver is preferably 8.8 or more, more preferably 8.9 or more, further preferably 9.0 or more, and preferably 9.6 or less, 9 5.5 or less is more preferable, and 9.4 or less is further preferable. The SP value of the base oil generally shows a value of about 8.0 to 8.5, but if the SP value of the polymer is 8.8 or more, the viscosity index of the lubricating oil composition can be easily increased, and the SP of the polymer can be easily increased. When the value is 9.6 or less, it becomes easy to secure the solubility of the viscosity index improver in the base oil.

The viscosity index improver of the present invention can achieve both the viscosity index improving effect and the shear stability at a high level. As specific numerical values of shear stability, SSI and decomposition start temperature obtained by the method shown below are indicators.

The SSI of the viscosity index improver is obtained by diluting the viscosity index improver (polymer) in the base oil so that the kinematic viscosity at 100 ° C. is 7.0 mm ² / sec, and the kinematic viscosity before and after the shearing treatment by the ultrasonic homogenizer. The kinematic viscosity of the base oil at 100 ° C. is measured and calculated by the following formula: SSI = {1- (kinematic viscosity after shearing treatment-kinematic viscosity of base oil) / (kinematic viscosity before shearing treatment-kinematic viscosity of base oil) )} × 100. The SSI of the viscosity index improver is preferably 38 or less, more preferably 36 or less, still more preferably 34 or less, which improves the shear stability and storage stability of the viscosity index improver. The lower limit of the SSI of the viscosity index improver is not particularly limited, but is preferably 0.1 or more, more preferably 0.5 or more, still more preferably 2 or more, still more preferably 5 or more. be. When the SSI is less than 0.1, the viscosity index improving effect of the viscosity index improving agent tends to decrease.

The viscosity index improver is the concentration of the viscosity index improver (polymer) in the base oil, which has a kinematic viscosity of 7.0 mm ² / sec at 100 ° C. when the viscosity index improver (polymer) is diluted with the base oil. The higher the value, the higher the viscosity index and shear stability tend to be, and the concentration thereof is preferably 3.0% by mass or more, more preferably 3.5% by mass or more. On the other hand, the upper limit of the concentration is not particularly limited, but may be, for example, 10.0% by mass or less.

The decomposition start temperature of the polymer contained in the viscosity index improver is preferably 290 ° C. or higher, more preferably 295 ° C. or higher, further preferably 300 ° C. or higher, particularly preferably 310 ° C. or higher, and further preferably 500 ° C. or lower. It is preferably 450 ° C. or lower, more preferably 400 ° C. or lower, and particularly preferably 380 ° C. or lower. By increasing the decomposition start temperature of the viscosity index improver, the heat resistance is improved, and the thermal decomposition stability and the shear stability are improved. On the other hand, when the heat resistance is excessively improved, the solubility of the viscosity index improver in the base oil tends to be insufficient, or the viscosity index tends to decrease.

The viscosity index improver preferably has a viscosity index of 200 or more when the viscosity index improver (polymer) is diluted with the base oil so that the kinematic viscosity at 100 ° C. is 7.0 mm ² / s. 230 or more is more preferable, 255 or more is further preferable, 350 or less is preferable, and 300 or less is more preferable. When the viscosity index of the viscosity index improver is within the above range, fuel efficiency, thermal / oxidation stability, and storage stability are excellent. The viscosity index is measured according to the method of JIS K 2283.

The viscosity index improver of the present invention contains the above-mentioned polymer as a main component, and preferably contains 70% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass of the polymer in 100% by mass of the viscosity index improver. It is contained in an amount of% by mass or more, particularly preferably 99% by mass or more. The viscosity index improver may be composed only of the above-mentioned polymer. Examples of the components other than the above-mentioned polymers contained in the viscosity index improver of the present invention include polymethacrylate, polyisobutylene, ethylene-propylene copolymers, styrene-diene hydride copolymers, graft polymers and comb polymers thereof. Examples include star-shaped polymers.

The polymer contained in the viscosity index improver of the present invention is a step of radically polymerizing a monomer component containing a macromonomer forming a unit (A) and an alkyl (meth) acrylate forming a unit (B) (polymerization step). ) Can be obtained by the production method having. As the macromonomer forming the unit (A), a commercially available one may be used, or a macromonomer may be synthesized by providing a macromonomer synthesis step prior to the polymerization step.

The polymerization method of the monomer component in the polymerization step may be, for example, bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc., but considering the handleability of the obtained polymer as a viscosity index improver, a solution. It is preferable to carry out the polymerization by polymerization. When a dispersion medium, an emulsifier, a dispersant or the like is used, there are no particular restrictions and known ones can be used.

In the polymerization step, a macromonomer forming the unit (A) and an alkyl (meth) acrylate forming the unit (B) are indispensably used as the monomer component, and an alkyl (meth) forming the unit (C) is further formed. An acrylate, a maleimide-based monomer forming the unit (D), and a monomer forming the unit (E) may be used as the monomer component.

The solvent used for the polymerization is not particularly limited as long as it is inert to the polymerization reaction, and the polymerization mechanism, the type and amount of the monomer used, the type and amount of the polymerization initiator and the polymerization catalyst, etc. It may be appropriately set according to the polymerization conditions of. From the viewpoint of ensuring the solubility of the polymer and the ease of solvent replacement with the base oil after the polymerization, toluene, xylene, hexane, cyclohexane, methyl ethyl ketone and tetrahydrofuran are preferable as the solvent used for the polymerization. Further, the lubricating oil base oil described later can also be suitably used as a solvent. In this case, solvent replacement after polymerization becomes unnecessary and the process is simplified, which is more preferable. Only one kind of these solvents may be used, or two or more kinds thereof may be used in combination. The amount of the solvent used is not particularly limited, but it is preferable that the concentration of the total amount of the monomer component, the polymerization initiator and other components is 40% by mass or more and 100% by mass or less of the whole.

It is preferable to use a polymerization initiator at the time of polymerization. A known polymerization initiator may be used as the polymerization initiator. For example, 2,2'-azobisisobutyronitrile, 2,2'-azobis (2-amidinopropane) dihydrochloride, dimethyl-2, Azo compounds such as 2'-azobis (2-methylpropionate) and 4,4'-azobis (4-cyanopentanoic acid); persulfates such as potassium persulfate; cumenehydroperoxide, diisopropylbenzenehydroperoxide , Di-t-butyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butylperoxyisopropyl carbonate, t-amylperoxy-2-ethylhexanoate, t-amylperoxyoctate, t-amylper Peroxides such as oxyisononanoate can be used. Moreover, the polyfunctional initiator described above can also be used. Only one of these may be used, or two or more thereof may be used in combination. The amount of the polymerization initiator used is preferably 0.01 to 3 parts by mass with respect to 100 parts by mass of the monomer component, for example.

In the polymerization step, a chain transfer agent or the like may be used. By using a chain transfer agent, it becomes easy to obtain a polymer having a small molecular weight distribution. In addition, thermal decomposition due to depolymerization can be easily suppressed. Chain transfer agents include butanethiol, octanethiol, octadecanethiol, dodecanethiol, cyclohexyl mercaptan, thiophenol, octyl thioglycolate, octyl 2-mercaptopropionate, octyl 3-mercaptopropionate, 2-ethylhexyl ester of mercaptopropionate. , Octanoic acid 2-mercaptoethyl ester, 1,8-dimercapto-3,6-dioxaoctane, dodecyl mercaptan, mercaptans such as ethylene glycol bisthioglycolate; carbon tetrachloride, carbon tetrabromide, methylene chloride, bromoform, Halogen compounds such as bromotrichloroethane; α-methylstyrene dimers and the like can be mentioned. Further, the polyfunctional chain transfer agent described above can also be used. The amount of the chain transfer agent used is preferably 0.01 to 3 parts by mass with respect to 100 parts by mass of the monomer component, for example.

The temperature of the polymerization reaction may be appropriately adjusted according to the type of the polymerization solvent and the degree of progress of the polymerization reaction. For example, 0 ° C. or higher is preferable, 25 ° C. or higher is more preferable, and 200 ° C. or lower is preferable. The following is more preferable. The time of the polymerization reaction may be appropriately adjusted according to the degree of progress of the polymerization reaction, and may be, for example, 1 to 48 hours (preferably 3 to 24 hours).

When the macromonomer synthesis step is performed, a compound having a macrohydrogen group described above and a functional group selected from a hydroxyl group, an amino group, a carboxy group, a carboxylic acid ester group, an isocyanate group, and a sulfo group (hereinafter referred to as a functional group). , "Macro compound") and a compound having a polymerizable double bond (hereinafter referred to as "counter compound") with a reactive group with the functional group can be reacted to synthesize a macromonomer. preferable. By reacting the macro compound and the counter compound (addition reaction or condensation reaction) and polymerizing the obtained macromonomer together with other monomer components in the polymerization step, the macrocarbonate derived from the macro compound is contained in the polymer. The group is taken in.

As the functional group of the macro compound, a hydroxyl group, a carboxy group, and a carboxylic acid ester group are preferable from the viewpoint of easy production and availability. The macro compound preferably has only one such functional group, and more preferably has such a functional group at the end of the macro compound.

Examples of the reactive group of the counter compound include a hydroxyl group, an amino group, a carboxy group, a carboxylic acid ester group, an isocyanate group, a sulfo group, and an oxazoline group. The counter compound preferably has only one such reactive group. Counter compounds include (meth) acrylates such as 2-isocyanatoethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and 3-sulfopropyl (meth) acrylate; (meth) acrylate; 2-hydroxyethyl. Vinyl ethers such as vinyl ether and 2,2-dimethyl-2-isocyanatoethyl vinyl ether; styrenes such as 4-aminostyrene and 4-vinylbenzenesulfonic acid; 2-isopropenyl-2-oxazoline and the like can be mentioned.

The reaction between the macro compound and the counter compound is a urethanization reaction in which an isocyanate group reacts with a hydroxyl group, a urea conversion reaction in which an isocyanate group reacts with an amino group, an esterification reaction in which a carboxy group reacts with a hydroxyl group, and a carboxy group and an amino reaction. Amidation reaction in which a group reacts, sulfonic acid esterification reaction in which a sulfo group reacts with a hydroxyl group, a sulfone amidation reaction in which a sulfo group reacts with an amino group, and an ester exchange reaction in which an esterified product of a hydroxyl group reacts with a carboxy group. , An amide esterification reaction in which an oxazoline group and a carboxy group react with each other. Among these, the urethanization reaction, the urea conversion reaction, the esterification reaction, the transesterification reaction, or the amidation reaction is preferable, and the urethanization reaction is particularly preferable from the viewpoint of excellent reactivity.

In the macromonomer synthesis step, it is preferable to carry out the reaction between the macro compound and the counter compound in the presence of a metal catalyst. As a result, the macromonomer can be efficiently produced from the macro compound and the counter compound, and the reaction time can be shortened. Further, in the subsequent polymerization step, even if the metal derived from the metal catalyst remains in the reaction solution, the polymerization reaction of the monomer component containing the macromonomer can be suitably carried out.

The metal catalyst is not particularly limited as long as it promotes the reaction between the macro compound and the counter compound, but is a metal catalyst containing one or more metal elements selected from the group consisting of titanium, zirconium, zinc, tin, and bismuth. Is preferable, and it is more preferable to use a titanium catalyst and / or a tin catalyst. If a titanium catalyst and / or a tin catalyst is used, the reaction between the macro compound and the counter compound proceeds rapidly in the macromonomer synthesis step, and the metal derived from these catalysts remains in the reaction solution in the subsequent polymerization step. Even so, the polymerization rate of the macromonomer can be increased, and it becomes easy to obtain a polymer having a higher molecular weight.

The metal catalyst preferably has a group or ligand containing a Group 16 element. In this case, it is preferable that the group 16 element contained in the group or the ligand is bonded or coordinated to the metal atom of the metal catalyst. Examples of the Group 16 element include oxygen, sulfur, selenium, tellurium and the like, and among them, a group or a ligand containing oxygen or sulfur is preferable. Examples of such a group or a ligand include an alkoxy group, an aryloxy group, an acyloxy group, an acylate group, a catecholate group, a thiol group, a thiocyanate group and the like, and a group or a ligand containing oxygen is particularly preferable. ..

The synthesis of macromonomers is preferably carried out in a solvent. As the solvent, a solvent that can be used in the polymerization reaction can be used, and a lubricating oil base oil can also be preferably used. The amount of the reaction solvent used in the macromonomer synthesis step is not particularly limited, but it is preferable that the total concentration of the macro compound and the counter compound in the reaction solution is 5% by mass or more and 70% by mass or less.

When the macromonomer is synthesized in the lubricating oil base oil, the lubricating oil base oil can also be used as the reaction solvent in the polymerization step. This simplifies the macromonomer synthesis step and the polymerization step, and eliminates the need for solvent substitution after polymerization, so that the viscosity index improver of the present invention can be easily produced. In this case, in the presence of the metal derived from the metal catalyst used in the macromonomer synthesis step, a polymerization step of polymerizing the monomer component containing the macromonomer in the solvent (lubricating oil base oil) used in the macromonomer synthesis step is performed. You may go.

The temperature at which the macro compound and the counter compound are reacted may be appropriately adjusted according to the type of reaction solvent and the degree of progress of the reaction. For example, 0 ° C. or higher is preferable, 25 ° C. or higher is more preferable, and 180 ° C. or higher is more preferable. The temperature is preferably 155 ° C or lower, more preferably 155 ° C or lower. The reaction time may be appropriately adjusted according to the degree of progress of the reaction, and may be, for example, 20 minutes to 16 hours (preferably 30 minutes to 12 hours).

[2. Composition containing viscosity index improver and base oil]
The present invention also provides a lubricating oil composition containing the viscosity index improver of the present invention. The viscosity index improver of the present invention can be blended with a lubricating oil base oil to form a lubricating oil composition. The lubricating oil composition may be used in the lubricating oil without being further diluted with the lubricating oil base oil, or may be further diluted with the lubricating oil base oil and used in the lubricating oil. In the latter case, the lubricating oil composition is used as a stock solution, which may be hereinafter referred to as "base oil composition".

As the lubricating oil base oil, known lubricating oil base oils can be used without particular limitation, and mineral oil-based base oils and synthetic base oils can be preferably mentioned. Examples of the mineral oil-based base oil include paraffin-based and naphthenic-based base oils. Mineral-based base oils include those obtained by solvent refining of raw material base oils, hydrogenation decomposition or hydrogenation isomerization treatment. Examples of the synthetic base oil include hydrocarbon-based, ester-based, ether-based, silicone-based, and fluorine-based base oils. As described above, the lubricating oil base oil can also be used as a polymerization reaction solvent for the polymer contained in the viscosity index improver.

As a preferable specific example of the mineral oil-based base oil, the following base oils (1) to (7) are used as raw materials, and the raw material oil and / or the lubricating oil distillate recovered from the raw material oil is used as a predetermined refining method. The base oil obtained by refining with and recovering the lubricating oil distillate can be mentioned. Further, the following base oil (8) or (9) obtained by performing a predetermined treatment on the base oil selected from (1) to (7) or the lubricating oil fraction recovered from the base oil is particularly preferable.

(1) Distilled oil (WVGO) by vacuum distillation of atmospheric distillation residual oil of paraffin-based crude oil and / or mixed-based crude oil.
(2) Wax (slack wax, etc.) obtained by the dewaxing process of lubricating oil and / or synthetic wax (Fischer-Tropsch wax, GTL wax, etc.) obtained by the gas to liquid (GTL) process, etc.
(3) One or more mixed oils selected from the base oils (1) to (2) and / or mild hydrocracking treated oils of the mixed oils (4) Base oils (1) to (3) Two or more mixed oils (5) Base oil (1) to any of (4) degreased oil (DAO)
(6) Mild hydrocracking treated oil (MHC) of base oil (5)
(7) Two or more mixed oils selected from the base oils (1) to (6) (8) The base oil selected from the above base oils (1) to (7) or the lubricating oil distiller recovered from the base oil. The fraction is hydrolyzed and decomposed, and the product or the lubricating oil distillate recovered from the product is subjected to dewaxing treatment such as solvent dewaxing or contact dewaxing, or distillation after the dewaxing treatment. Hydrolyzed mineral oil obtained by doing so.
(9) The base oil selected from the above base oils (1) to (7) or the lubricating oil fraction recovered from the base oil is hydroisomerized and recovered from the product or the product by distillation or the like. A hydride isomerized mineral oil obtained by performing a dewaxing treatment such as solvent dewaxing or contact dewaxing on a lubricating oil fraction, or by distilling after the dewaxing treatment.

Specific examples of the synthetic base oil include poly-α-olefins or hydrides thereof, isobutene oligomers or hydrides thereof, isoparaffin, alkylbenzenes, alkylnaphthalene, and diesters (ditridecylglutarate, di-2-ethylhexyl adipate, diisodecyl). Adipate, ditridecyl adipate, di-2-ethylhexyl sebacate, etc.), polyol ester (trimethylolpropane caprilate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, etc.), polyoxyalkylene Examples thereof include glycol, dialkyldiphenyl ether, polyphenyl ether and the like, and among them, poly α-olefin is preferable. The poly-α-olefin is typically an α-olefin oligomer or co-oligomer having 2 to 32 carbon atoms, preferably 6 to 16 carbon atoms (1-octene oligomer, decene oligomer, ethylene-propylene co-oligomer, etc.) and them. The hydride of is mentioned.

The kinematic viscosity of the lubricating oil base oil such as the mineral base oil and the synthetic base oil described above at 100 ° C. is preferably 1 to 20 mm ² / s.

As the lubricating oil base oil to be blended in the lubricating oil composition, the base oil selected from the above-mentioned base oils (1) to (7) or the lubricating oil distillate recovered from the base oil is subjected to the above-mentioned treatment. The obtained base oil (8) or (9) is preferable. It is also preferable to use a base oil belonging to Group III based on the classification by the American Petroleum Institute (API). As the lubricating oil base oil to be blended in the lubricating oil composition, the above-mentioned synthetic base oil may be used.

In the lubricating oil composition of the present invention, the above-mentioned lubricating oil base oil may be used alone, or may be used in combination with one or more of other base oils. When the lubricating oil base oil and another base oil are used in combination to form a mixed base oil, it is preferable that the mixed base oil contains at least the above-mentioned lubricating oil base oil (8) or (9). The ratio of the lubricating oil base oil (8) or (9) in the mixed base oil is preferably 30% by mass or more, more preferably 50% by mass or more, and more preferably 70% by mass or more. More preferred.

The viscosity index of the lubricating oil base oil is preferably 100 or more, more preferably 120 or more, and preferably 160 or less. If the viscosity index is less than the above lower limit, not only the viscosity-temperature characteristics, thermal / oxidation stability, and volatilization prevention property deteriorate, but also the friction coefficient tends to increase and the wear prevention property decreases. There is a tendency. Further, when the viscosity index exceeds the above upper limit value, the low temperature viscosity characteristic tends to deteriorate. The viscosity index referred to in the present invention means a viscosity index measured in accordance with JIS K 2283.

The viscosity index of the lubricating oil composition is preferably 200 or more, more preferably 230 or more, further preferably 255 or more, more preferably 350 or less, and even more preferably 300 or less. When the viscosity index is within the above range, fuel efficiency, thermal / oxidation stability, and storage stability are excellent.

The content of the polymer according to the present invention in the lubricating oil composition is not particularly limited, and for example, 0.01 part by mass or more is preferable, and 0.1 part by mass or more is more preferable in 100 parts by mass of the lubricating oil composition. , 0.5 parts by mass or more, more preferably 70 parts by mass or less, more preferably 60 parts by mass or less, still more preferably less than 50 parts by mass. When the lubricating oil composition is used for the lubricating oil without being further diluted with the lubricating oil base oil, the content of the polymer according to the present invention in the lubricating oil composition is 100 parts by mass of the lubricating oil composition. 0.01 parts by mass or more is preferable, 0.1 parts by mass or more is more preferable, 0.5 parts by mass or more is further preferable, 20 parts by mass or less is more preferable, 15 parts by mass or less is more preferable, and 10 parts by mass or less is more preferable. More preferred. When the lubricating oil composition of the present invention is used as the base oil composition, the content of the polymer according to the present invention in the base oil composition is preferably 5 parts by mass or more, for example, 5 parts by mass in 100 parts by mass of the lubricating oil composition. 10 parts by mass or more is more preferable, 20 parts by mass or more is further preferable, 70 parts by mass or less is more preferable, 60 parts by mass or less is more preferable, and less than 50 parts by mass is further preferable.

The lubricating oil composition of the present invention contains the viscosity index improver of the present invention and the lubricating oil base oil as essential components, and may further contain any additive or the like. Lubricating oil compositions include, for example, flow point depressants, anti-wear agents, metal-based cleaning dispersants, ashless cleaning dispersants, antioxidants, corrosion inhibitors, defoamers, friction modifiers, rust inhibitors, anti-corrosion agents. It is preferable that at least one additive selected from the group consisting of an emulsifier and a metal inactivating agent is blended.

As the pour point depressant, any pour point depressant used for lubricating oil can be used. Examples of the pour point lowering agent include polymethacrylates, naphthalene-chlorinated paraffin condensation product, phenol-chlorinated paraffin condensation product and the like. Of these, polymethacrylates are preferred.

As the anti-wear agent (or extreme pressure agent), any anti-wear agent / extreme pressure agent used for lubricating oil can be used. As the anti-wear agent (or extreme pressure agent), for example, sulfur-based, phosphorus-based, sulfur-phosphorus-based extreme pressure agents and the like can be used, and specifically, zinc dialkyldithiophosphate (ZnDTP) and phosphite ester. , Thio-phosphate esters, dithio-phosphate esters, trithio-phosphate esters, phosphate esters, thiophosphate esters, dithiophosphate esters, trithiophosphate esters, amine salts thereof, these Examples thereof include metal salts, derivatives thereof, dithiocarbamates, zinc dithiocarbamates, MoDTC, disulfides, polysulfides, sulphide olefins, sulphurized fats and oils and the like. Among these, sulfur-based extreme pressure agents are preferable, and sulfurized fats and oils are particularly preferable.

Examples of the metal-based cleaning dispersant include normal salts or basic salts such as alkali metal / alkaline earth metal sulfonate, alkali metal / alkaline earth metal phenate, and alkali metal / alkaline earth metal salicylate. Examples of the alkali metal include sodium and potassium, and examples of the alkaline earth metal include magnesium, calcium and barium, but magnesium or calcium is preferable, and calcium is more preferable.

As the ashless cleaning dispersant, any ashless cleaning dispersant used for lubricating oil can be used. Examples of the ashless cleaning dispersant include mono or biscosuccinate imide having at least one linear or branched alkyl group or alkenyl group having 40 to 400 carbon atoms in the molecule, and an alkyl group having 40 to 400 carbon atoms. Alternatively, a benzylamine having at least one alkenyl group in the molecule, an alkyl group having 40 to 400 carbon atoms or a polyamine having at least one alkenyl group in the molecule, or a modification due to these boron compounds, carboxylic acid, phosphoric acid, etc. Examples include products. At the time of use, one kind or two or more kinds arbitrarily selected from these can be blended.

Examples of the antioxidant include ashless antioxidants such as phenol and amines, and metal-based antioxidants such as copper and molybdenum. Examples of the antioxidant include 4,4'-methylenebis (2,6-di-tert-butylphenol) and 4,4'-bis (2,6-di-tert) as the phenolic ashless antioxidant. -Butylphenol) and the like, examples of the amine-based ashless antioxidant include phenyl-α-naphthylamine, alkylphenyl-α-naphthylamine, dialkyldiphenylamine and the like.

Examples of the corrosion inhibitor include benzotriazole-based, triltriazole-based, thiadiazole-based, and imidazole-based compounds.

Examples of the defoaming agent include silicone oils having a kinematic viscosity of 1000 to 100,000 mm ² / s at 25 ° C., fluorosilicone oils, alkenylsuccinic acid derivatives, polyhydroxyfatty alcohols and long-chain fatty acid esters, and methylsalicy. Examples include rates and o-hydroxybenzyl alcohol.

Friction modifiers include succinic imide molybdenum complexes such as molybdenum dithiocarbamate and molybdenum dithiophosphate, organic molybdenum compounds such as amine salts of organic molybdenum acid, and linear alkyls and metals with 8 to 30 carbon atoms as basic structures. Examples thereof include those having a structure having a polar group that can be adsorbed on molybdenum in the same molecule. Polar groups include amines, polyamines, amides, amine compounds, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, aliphatic ethers, urea compounds, hydrazide compounds, etc. that have these in the molecule at the same time. Examples thereof include succinic acid imide type, ester, alcohol or diol, or monoalkyl glycerin ester having an ester and a hydroxyl group at the same time. In addition, there are various types such as an alkylamine alkoxyalcohol having an amine and a hydroxyl group in the same molecule.

Examples of the rust preventive agent include petroleum sulfonate, alkylbenzene sulfonate, dinonylnaphthalene sulfonate, alkenyl succinic acid ester, polyhydric alcohol ester and the like.

Examples of the anti-emulsifier include polyalkylene glycol-based nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene alkyl naphthyl ether.

Examples of the metal inactivating agent include imidazoline, pyrimidine derivative, alkylthiadiazole, mercaptobenzothiazole, benzotriazole or its derivative, 1,3,4-thiadiazole polysulfide, 1,3,4-thiadiazole-2,5-bis. Examples thereof include dialkyldithiocarbamate, 2- (alkyldithio) benzimidazole, β- (o-carboxybenzylthio) propionnitrile and the like.

Lubricating oil composition is a flow point lowering agent, anti-wear agent, metal-based cleaning dispersant, ashless cleaning dispersant, antioxidant, corrosion inhibitor, foam eliminator, friction modifier, rust inhibitor, anti-emulsifier, When one or more selected from the group consisting of the metal inactivating agent and the metal inactivating agent is contained, the content of each is, for example, 0.01 part by mass or more and 10 parts by mass or less in 100 parts by mass of the lubricating oil composition. It should be.

When the lubricating oil composition contains a metal-based cleaning dispersant, the content thereof is preferably 0.01 parts by mass or more and less than 30 parts by mass in 100 parts by mass of the lubricating oil composition. If the content is less than 0.01 parts by mass, the fuel saving effect may last only for a short period of time, and if it is 30 parts by mass or more, it becomes difficult to obtain an effect commensurate with the content.

When the lubricating oil composition contains a foam eliminating agent, the content thereof is preferably 0.0001 part by mass or more and 0.01 part by mass or less in 100 parts by mass of the lubricating oil composition.

When the lubricating oil composition contains a friction modifier, the content thereof is preferably 0.01 part by mass or more and 3 parts by mass or less in 100 parts by mass of the lubricating oil composition. If the content of the friction modifier is less than 0.01 parts by mass, the friction reducing effect due to its addition tends to be insufficient, and if it exceeds 3 parts by mass, the effect of other additives tends to be hindered. Or the solubility of the additive tends to deteriorate.

When the lubricating oil composition is used as the base oil composition, the base oil composition may substantially consist of a viscosity index improver and a lubricating oil base oil, in which case the viscosity in the base oil composition. The total content of the index improver and the lubricating oil base oil is preferably, for example, 98 parts by mass or more, more preferably 99 parts by mass or more, and further preferably 99.5 parts by mass or more in 100 parts by mass of the base oil composition. preferable. In particular, it is preferable that the base oil composition is configured so that the total content of the polymer and the lubricating oil base oil described above is in such a range.

In addition to the above components, the lubricating oil composition can contain a viscosity index improver other than the polymer of the present invention. The viscosity index improver other than the polymer of the present invention is specifically a non-dispersion type or dispersion type ester group-containing viscosity index improver, and for example, a non-dispersion type or dispersion type poly (meth) acrylate-based viscosity index improvement agent. Examples thereof include a non-dispersion type or a dispersion type olefin- (meth) acrylate copolymerization system viscosity index improver, a styrene-maleic anhydride copolymer polymerization system viscosity index improver, and a mixture thereof. Among these, a non-dispersive or dispersed poly (meth) acrylate-based viscosity index improver is preferable, and a non-dispersive or dispersed polymethacrylate-based viscosity index improver is more preferable. Other examples include non-dispersive or dispersed ethylene-α-olefin copolymers or hydrides thereof, polyisobutylene or hydrides thereof, styrene-diene hydride copolymers and polyalkylstyrenes.

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

(1) Analysis and evaluation method (1-1) Polymerization rate The polymerization rate of each monomer component was determined by using gas chromatography (manufactured by Shimadzu Corporation, GC-2010plus). Specifically, a calibration curve solution in which each monomer and tridecane were dissolved in ethyl acetate was prepared, measured by gas chromatography, and a calibration curve was prepared from the peak area. Then, a sample solution in which the polymer solution and tridecane were dissolved in ethyl acetate was prepared and measured by gas chromatography in the same manner. The polymerization rate of each monomer component was determined by the internal standard method. The measurement conditions for gas chromatography are shown below.
-Column: Inert Cap1 manufactured by GL Science (film thickness of liquid phase: 0.25 μm, length: 30 m, inner diameter: 0.25 mm)
-Temperature: 40 ° C (hold for 5 minutes) + 40 ° C to 170 ° C (10 ° C / min) + 170 ° C to 210 ° C (5 ° C / min) + 210 ° C to 330 ° C (15 ° C / min) + 330 ° C (hold for 20 minutes)
-Vaporization room temperature: 200 ° C
-Detector temperature: 350 ° C (FID)
-Carrier gas: Helium (column flow rate 1.33 mL / min)
-Injection volume: 0.5 μL (split method, split ratio: 30.0)
-Internal standard sample: Tridecane-Diluting solvent: Ethyl acetate

(1-2) Weight average molecular weight and number average molecular weight The weight average molecular weight and the number average molecular weight of the polymer were determined by using gel permeation chromatography (HLC-8320GPC ECOSEC, manufactured by Tosoh Corporation). The measurement conditions are as follows.
-Column: TSKgel GMHXL 2 bottles manufactured by Tosoh Co., Ltd.-Developing solvent: Tetrahydrofuran-Flow rate of developing solvent: 1.0 mL / min-Standard sample: TSK standard polystyrene (PS-oligomer kit manufactured by Tosoh Corporation)
-Column temperature: 40 ° C
-Sample concentration: 0.5%
-Injection volume: 200 μL

(1-3) Solubility of base oil 2 parts by mass of the polymer and 98 parts by mass of the base oil (YUBASE4 manufactured by SK) are mixed to prepare a base oil solution of the polymer, and the mixture is stirred at 80 ° C. for 30 minutes. Heated. Then, the base oil solution of the polymer was cooled to room temperature, and the presence or absence of precipitates was visually confirmed. When the precipitate was confirmed, it was evaluated as solubility ×, and when the precipitate was not confirmed, it was evaluated as solubility ○. YUBASE4 manufactured by SK is a Group III base oil (viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² / s) in the American Petroleum Institute (API) classification.

(1-4) Viscosity index The polymer was diluted with a base oil (YUBASE4, manufactured by SK) so that the kinematic viscosity at 100 ° C. was 7.0 mm ² / s, and the measurement was carried out by the method of JIS K 2283.

(1-5) Shear Stability A base oil solution of the polymer was prepared by diluting the polymer with a base oil (YUBASE4, manufactured by SK) so that the kinematic viscosity at 100 ° C. was 7.0 mm ² / s. While keeping this at 100 ° C., an ultrasonic homogenizer (Hielscher UP400S manufactured by Ultrasonics) was used to apply ultrasonic waves under the conditions of Amplitude = 70% and Cycle = 1 for 10 minutes for shearing. The kinematic viscosities of the polymer base oil solution and the base oil before and after the shearing treatment were measured at 100 ° C., and the shear stability (SSI) was obtained by the following formula: SSI = {1- (kinematic viscosity after the shearing treatment-). Base oil kinematic viscosity) / (kinematic viscosity before shearing-base oil kinematic viscosity)} × 100. When the SSI value was 38 or less, it was evaluated as ◯, and when it exceeded 38, it was evaluated as x.

(1-6) Viscosity The base oil solution of the polymer obtained in the Example or Comparative Example is diluted with the base oil to add 20% by mass of the polymer (including the polymer raw material), classified by the American Petroleum Association (API). Prepared a base oil solution of a polymer containing Group III base oil (SK, YUBASE4, viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² / s) in a proportion of 80% by mass, and prepared a viscous meter (Toki). The viscosity of the base oil solution of the polymer was measured under the condition of 25 ° C. by TVE-35H manufactured by Sangyo Co., Ltd., 3 ° × R9.7 rotor, rotation speed 50 rpm). When the viscosity was 25 Pa · s or less, it was evaluated as ◯, and when it exceeded 25 Pa · s, it was evaluated as ×.

(2) Production example of macromonomer (2-1) Production of macromonomer 1 One-ended hydroxyl group-containing weight of hydride polybutadiene in a reaction vessel equipped with a stirrer, temperature sensor, cooling tube, nitrogen introduction tube, and dropping funnel. 50 parts by mass of coalescence (KrasolHLBH-5000M, manufactured by TOTAL), 1.6 parts by mass of 2-isocyanatoethyl methacrylate (Carens MOI, manufactured by Showa Denko), 20 parts by mass of toluene, 0.1 part by mass of dibutyltin dilaurylate. The mixture was charged and stirred for 6 hours while being heated to 65 ° C. in an oil bath while introducing nitrogen gas. After completion of the reaction, 50 parts by mass of water was added, and the supernatant was recovered by a separating funnel. After raising the temperature to 65 ° C., toluene was removed under reduced pressure to obtain 48 parts by mass of macromonomer 1 shown in Table 1. ..

The obtained macromonomer 1 was dissolved in deuterated chloroform (manufactured by Wako Pure Chemical Industries, Ltd.), and ¹ H-NMR measurement was performed using a nuclear magnetic resonance spectrometer (manufactured by Varian, Unity Plus 400). A ¹ H-NMR chart of macromonomer 1 is shown in FIG. A peak near 3.9 ppm attributed to the alcohol group of the raw material was not confirmed, and a peak around 4.9 ppm attributed to the produced urethane group was confirmed.

(2-2) Production of Macromonomer 2 In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel, a polymer containing a single-ended hydroxyl group of hydride polybutadiene (manufactured by TOTAL, KrasolHLBH-). 5000M) 50 parts by mass, 3.0 parts by mass of methacrylic anhydride, 10 parts by mass of toluene, and 2.5 parts by mass of pyridine were charged, and these were heated under reflux at 100 ° C. using an oil bath while introducing nitrogen gas16. Time stirring was performed. After completion of the reaction, 50 parts by mass of a 20 mass% sodium hydrogen carbonate aqueous solution was added, and the mixture was heated under reflux at 80 ° C. for 10 minutes, and the supernatant was recovered by a separating funnel. After raising the temperature of the supernatant to 65 ° C., toluene was removed under reduced pressure to obtain 38 parts by mass of macromonomer 2 shown in Table 1.

The obtained macromonomer 2 was dissolved in deuterated chloroform (manufactured by Wako Pure Chemical Industries, Ltd.), and ¹ H-NMR measurement was performed using a nuclear magnetic resonance spectrometer (manufactured by Varian, Unity Plus 400). A ¹ H-NMR chart of macromonomer 2 is shown in FIG. A peak near 3.9 ppm attributed to the alcohol group of the raw material was not confirmed, and a peak around 5.1 ppm attributed to the produced ester group was confirmed.

(3) Production Example of Base Oil Solution of Polymer (3-1) Example 1
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel, 12 parts by mass of macromonomer 1, 67 parts by mass of n-butyl methacrylate (BMA), and lauryl methacrylate were added as monomer components. / Tridecyl methacrylate mixture (mass ratio = 54/46) (SLMA) 21 parts by mass, and base oil (SK, YUBASE4) 124.2 parts by mass and pentaerythritol tetrakis (mercaptoacetate) 0.05 parts by mass. The temperature of the contents was raised to 105 ° C. while stirring while introducing nitrogen gas into the mixture. There, 0.1161 parts by mass of t-amylperoxyisononanoate (manufactured by Alchema Yoshitomi, Luperox (registered trademark) 570) and 8.2 parts by mass of base oil (manufactured by SK, YUBASE4) were added as a polymerization initiator. In addition to adding the mixed solution, 0.051 part by mass of t-amylperoxy-2-ethylhexanoate (manufactured by Alchema Yoshitomi, Luperox (registered trademark) 575) as a polymerization initiator is used as a base oil (manufactured by SK, Inc., YUBASE4) Solution polymerization was allowed to proceed while dropping the solution dissolved in 3.4 parts by mass over 2 hours, and further aging was carried out for 4 hours. Subsequently, 97.3 parts by mass of a base oil (YUBASE4 manufactured by SK) was added thereto and diluted to obtain a base oil solution of the polymer 1 (polymer concentration 30% by mass). Table 2 shows the composition ratio of the units derived from each monomer of the obtained polymer 1 and the analysis / evaluation results.

(3-2) Example 2
In Example 1, 12 parts by mass of macromonomer 1, 60 parts by mass of BMA, 23 parts by mass of stearyl methacrylate (SMA), and 5 parts by mass of N-phenylmaleimide (PMI) were used as the monomer components, and t-amylperoxy was used. 0.1161 parts by mass of isononanoate is 0.0774 parts by mass, and 0.051 part by mass of t-amylperoxy-2-ethylhexanoate is t-amylperoxyisononanoate (manufactured by Alchema Yoshitomi, Luperox (manufactured by Alchema Yoshitomi). A base oil solution of the polymer 2 (polymer concentration 30% by mass) was obtained by performing the same operation as in Example 1 except that the registered trademark) 570) was changed to 0.034 parts by mass. Table 2 shows the composition ratio of the units derived from each monomer of the obtained polymer 2 and the analysis / evaluation results.

(3-3) Example 3
In Example 2, 60 parts by mass of BMA was changed to 65 parts by mass and 23 parts by mass of SMA was changed to 18 parts by mass. 30% by mass) was obtained. Table 2 shows the composition ratio of the units derived from each monomer of the obtained polymer 3 and the analysis / evaluation results.

(3-4) Example 4
In Example 2, the base oil solution of the polymer 4 (polymer concentration 30% by mass) was performed in the same manner as in Example 2 except that 12 parts by mass of the macromonomer 2 was used instead of the macromonomer 1. %) Was obtained. Table 2 shows the composition ratio of the units derived from each monomer of the obtained polymer 4 and the analysis / evaluation results.

(3-5) Example 5
In Example 2, the same operation as in Example 2 is performed except that 12 parts by mass of macromonomer 1, 52 parts by mass of BMA, 21 parts by mass of SMA, and 10 parts by mass of methyl methacrylate (MMA) are used as the monomer components. As a result, a base oil solution of the polymer 5 (polymer concentration 30% by mass) was obtained. Table 2 shows the composition ratio of the units derived from each monomer of the obtained polymer 5 and the analysis / evaluation results.

(3-6) Example 6
In a reaction vessel equipped with a stirrer, temperature sensor, cooling tube, nitrogen introduction tube, and dropping funnel, 11.7 parts by mass, 2- Isocyanatoethyl methacrylate (manufactured by Showa Denko Co., Ltd., Karens MOI) 0.38 parts by mass, base oil (manufactured by SK Co., Ltd., YUBASE4) 73.6 parts by mass, tetraoctyl titanate (manufactured by Matsumoto Fine Chemical Co., Ltd., Olga Chix TA-30) 0 .024 parts by mass was charged, and the mixture was stirred for 30 minutes while heating at 75 ° C. in an oil bath while introducing nitrogen gas to obtain 85.7 parts by mass of the base oil solution of macromonomer 1 shown in Table 1. .. The obtained base oil solution of macromonomer 1 was dissolved in deuterated chloroform (manufactured by Wako Pure Chemical Industries, Ltd.), and ¹ H-NMR measurement was performed using a nuclear magnetic resonance spectrometer (manufactured by Varian, Unity Plus 400). .. A peak near 3.9 ppm attributed to the alcohol group of the raw material was not confirmed, and a peak around 4.9 ppm attributed to the produced urethane group was confirmed.
Next, 85.7 parts by mass of the obtained base oil solution of macromonomer 1 was placed in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel, n-butyl methacrylate (BMA). 60 parts by mass, 23 parts by mass of lauryl methacrylate / tridecyl methacrylate mixture (mass ratio = 54/46) (SLMA), 5 parts by mass of N-phenylmaleimide (PMI), and base oil (SK, YUBASE4) 151. .9 parts by mass and 0.05 parts by mass of pentaerythritol tetrakis (mercaptoacetate) were charged, and the temperature of the contents was raised to 105 ° C. while stirring while introducing nitrogen gas into the mixture. There, 0.0521 parts by mass of t-amylperoxyisononanoate (manufactured by Alchema Yoshitomi, Luperox (registered trademark) 570) and 5.1 parts by mass of base oil (manufactured by SK, YUBASE4) were added as a polymerization initiator. In addition to adding the mixed solution, 0.205 parts by mass of t-amylperoxyisononanoate (manufactured by Alchema Yoshitomi, Luperox (registered trademark) 570) as a polymerization initiator is used as a base oil (manufactured by SK, YUBASE4) 13. Solution polymerization was allowed to proceed while dropping the solution dissolved in 7 parts by mass over 4 hours, and aging was further carried out for 2 hours. Subsequently, 9.9 parts by mass of a base oil (YUBASE4 manufactured by SK) was added thereto and diluted to obtain a base oil solution of the polymer 6 (polymer concentration 28% by mass). Table 2 shows the composition ratio of the units derived from each monomer of the obtained polymer 6 and the analysis / evaluation results.

(3-7) Example 7
In Example 6, 60 parts by mass of BMA was changed to 62 parts by mass, 5 parts by mass of PMI was changed to 3 parts by mass, and 151.9 parts by mass of the base oil added during the polymerization reaction was changed to 136.1 parts by mass, and diluted after aging. By performing the same operation as in Example 6 except that 9.9 parts by mass of the base oil to be added to was changed to 30.8 parts by mass, a base oil solution of the polymer 7 (polymer concentration 28% by mass) was obtained. rice field. Table 2 shows the composition ratio of the units derived from each monomer of the obtained polymer 7 and the analysis / evaluation results.

(3-8) Example 8
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel, a polymer containing a single-ended hydroxyl group (TOTAL, Krasol HLBH-5000M), 9.7 parts by mass, 2- Isocyanatoethyl methacrylate (manufactured by Showa Denko Co., Ltd., Karenz MOI) 0.31 part by mass, base oil (manufactured by SK Co., Ltd., YUBASE4) 60 parts by mass, tetraoctyl titanate (manufactured by Matsumoto Fine Chemical Co., Ltd., Olgatics TA-30) 0.020 A mass portion was charged, and the mixture was stirred for 30 minutes while heating at 75 ° C. in an oil bath while introducing nitrogen gas to obtain 71.5 parts by mass of a base oil solution of macromonomer 1 shown in Table 1.
Next, in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel, 71.5 parts by mass of the obtained base oil solution of macromonomer 1 was added to n-butyl methacrylate (BMA). 65 parts by mass of stearyl methacrylate (SMA), 5 parts by mass of N-phenylmaleimide (PMI), 145.8 parts by mass of base oil (YUBASE4 manufactured by SK) and 0 parts of pentaerythritol tetrakis (mercaptoacetate). A 0.05 part by mass was charged, and the content was heated to 105 ° C. while stirring while introducing nitrogen gas into the mixture. There, 0.0521 parts by mass of t-amylperoxyisononanoate (manufactured by Alchema Yoshitomi, Luperox (registered trademark) 570) and 5.1 parts by mass of base oil (manufactured by SK, YUBASE4) were added as a polymerization initiator. In addition to adding the mixed solution, 0.205 parts by mass of t-amylperoxyisononanoate (manufactured by Alchema Yoshitomi, Luperox (registered trademark) 570) as a polymerization initiator is used as a base oil (manufactured by SK, YUBASE4) 13. Solution polymerization was allowed to proceed while dropping the solution dissolved in 7 parts by mass over 4 hours, and aging was further carried out for 2 hours. Subsequently, 30.8 parts by mass of a base oil (YUBASE4 manufactured by SK) was added thereto and diluted to obtain a base oil solution of the polymer 8 (polymer concentration 28% by mass). Table 2 shows the composition ratio of the units derived from each monomer of the obtained polymer 8 and the analysis / evaluation results.

(3-9) Example 9
In Example 8, the base oil solution (polymer concentration) of the polymer 9 was carried out in the same manner as in Example 8 except that 65 parts by mass of BMA was changed to 67 parts by mass and 5 parts by mass of PMI was changed to 3 parts by mass. 28% by mass) was obtained. Table 2 shows the composition ratio of the units derived from each monomer of the obtained polymer 9 and the analysis / evaluation results.

(3-10) Example 10
In a reaction vessel equipped with a stirrer, temperature sensor, cooling tube, nitrogen introduction tube, and dropping funnel, 14.6 parts by mass, 2- Isocyanatoethyl methacrylate (manufactured by Showa Denko Co., Ltd., Karenz MOI) 0.47 parts by mass, base oil (manufactured by SK Co., Ltd., YUBASE4) 92 parts by mass, tetraoctyl titanate (manufactured by Matsumoto Fine Chemical Co., Ltd., Olgatics TA-30) 0.030 A mass portion was charged, and the mixture was stirred for 30 minutes while heating at 75 ° C. in an oil bath while introducing nitrogen gas to obtain 107.1 parts by mass of a base oil solution of macromonomer 1 shown in Table 1. Subsequently, in Example 8, the amount of the base oil solution of the macromonomer 1 used was changed from 71.5 parts by mass to 107.1 parts by mass, 65 parts by mass of BMA was changed to 60 parts by mass, and 20 parts by mass of SMA was changed to 20 parts by mass of SLMA. By performing the operations after the polymerization reaction in the same manner as in Example 8 except that the 145.8 parts by mass of the base oil added during the polymerization reaction was changed to 117.7 parts by mass, the base oil solution of the polymer 10 ( Polymer concentration 28% by mass) was obtained. Table 2 shows the composition ratio of the units derived from each monomer of the obtained polymer 10 and the analysis / evaluation results.

(3-11) Example 11
In a reaction vessel equipped with a stirrer, temperature sensor, cooling tube, nitrogen introduction tube, and dropping funnel, 11.7 parts by mass, 2- Isocyanatoethyl methacrylate (manufactured by Showa Denko Co., Ltd., Karens MOI) 0.38 parts by mass, base oil (manufactured by SK Co., Ltd., YUBASE4) 73.6 parts by mass, tetraoctyl titanate (manufactured by Matsumoto Fine Chemical Co., Ltd., Olga Chix TA-30) 0 .024 parts by mass was charged, and the mixture was stirred for 30 minutes while heating at 75 ° C. in an oil bath while introducing nitrogen gas to obtain 85.7 parts by mass of the base oil solution of macromonomer 1 shown in Table 1. ..
Next, 85.7 parts by mass of the obtained base oil solution of macromonomer 1 was placed in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, a nitrogen introduction tube, and a dropping funnel, n-butyl methacrylate (BMA). 37 parts by mass of stearyl methacrylate (SMA), 6 parts by mass of N-phenylmaleimide (PMI), 89.6 parts by mass of base oil (SK, YUBASE4) and 0 parts of pentaerythritol tetrakis (mercaptoacetate) A 0.05 part by mass was charged, and the content was heated to 105 ° C. while stirring while introducing nitrogen gas into the mixture. There, 0.0521 parts by mass of t-amylperoxyisononanoate (manufactured by Alchema Yoshitomi, Luperox (registered trademark) 570) and 5.1 parts by mass of base oil (manufactured by SK, YUBASE4) were added as a polymerization initiator. In addition to adding the mixed solution, 0.205 parts by mass of t-amylperoxyisononanoate (manufactured by Alchema Yoshitomi, Luperox (registered trademark) 570) as a polymerization initiator is used as a base oil (manufactured by SK, YUBASE4) 13. A mixed solution of a solution dissolved in 7 parts by mass and a mixed solution of 25 parts by mass of BMA and 2 parts by mass of PMI as a dropping monomer component was added dropwise over 4 hours and 2 hours, respectively, to proceed with solution polymerization, and further aging for 2 hours. Was done. Subsequently, 30.8 parts by mass of a base oil (YUBASE4 manufactured by SK) was added thereto and diluted to obtain a base oil solution (polymer concentration 28% by mass) of the polymer 11. Table 2 shows the composition ratio of the units derived from each monomer of the obtained polymer 11 and the analysis / evaluation results.

(3-12) Example 12
In Example 6, 5 parts by mass of PMI is changed to 5 parts by mass of N-cyclohexylmaleimide (CHMI), and 151.9 parts by mass of the base oil added during the polymerization reaction is changed to 117.7 parts by mass, and the mixture is added to the dilution after aging. By performing the same operation as in Example 6 except that 9.9 parts by mass of the base oil was changed to 92.0 parts by mass, a base oil solution of the polymer 12 (polymer concentration 25% by mass) was obtained. Table 3 shows the composition ratio of the units derived from each monomer of the obtained polymer 12 and the analysis / evaluation results.

(3-13) Example 13
In Example 6, 60 parts by mass of BMA, 5 parts by mass of PMI is 5 parts by mass of CHMI, 23 parts by mass of SLMA is 18 parts by mass, and 151.9 parts by mass of base oil added during the polymerization reaction is 136.1 parts by mass. By performing the same operation as in Example 6 except that 9.9 parts by mass of the base oil added to the dilution after aging was changed to 73.6 parts by mass, the base oil solution of the polymer 13 ( Polymer concentration 25% by mass) was obtained. Table 3 shows the composition ratio of the units derived from each monomer of the obtained polymer 13 and the analysis / evaluation results.

(3-14) Example 14
In Example 6, 85.7 parts by mass, 55 parts by mass of BMA, 23 parts by mass of SLMA, 5 parts by mass of PMI, and 5 parts by mass of CHMI were charged as monomer components in the base oil solution of macromonomer 1 and polymerized. Example 6 except that 151.9 parts by mass of the base oil added during the reaction was changed to 136.1 parts by mass and 9.9 parts by mass of the base oil added to the dilution after aging was changed to 73.6 parts by mass. By performing the same operation as in the above, a base oil solution of the polymer 14 (polymer concentration 25% by mass) was obtained. Table 3 shows the composition ratio of the units derived from each monomer of the obtained polymer 14 and the analysis / evaluation results.

(3-15) Example 15
By performing the same operation as in Example 14 except that 5 parts by mass of CHMI was changed to 5 parts by mass of cyclohexyl methacrylate (CHMA) in Example 14, the base oil solution of the polymer 15 (polymer concentration 28% by mass) was performed. Got Table 3 shows the composition ratio of the units derived from each monomer of the obtained polymer 15 and the analysis / evaluation results.

(3-16) Example 16
In Example 6, 60 parts by mass of BMA is 67 parts by mass, 23 parts by mass of SLMA is 13 parts by mass of SMA, 5 parts by mass of PMI is 8 parts by mass of CHMI, and 151.9 parts by mass of base oil added during the polymerization reaction is 117.7 parts by mass. By performing the same operation as in Example 6 except that 9.9 parts by mass of the base oil to be added to the dilution after aging was changed to 49.1 parts by mass, the base oil solution of the polymer 16 (polymer). A concentration of 28% by mass) was obtained. Table 3 shows the composition ratio of the units derived from each monomer of the obtained polymer 16 and the analysis / evaluation results.

(3-17) Comparative Example 1
By performing the same operation as in Example 1 except that 71 parts by mass of BMA and 29 parts by mass of SLMA were used as the monomer components in Example 1, the base oil solution of the polymer 17 (polymer concentration 30% by mass) was performed. ) Was obtained. Table 3 shows the composition ratio of the units derived from each monomer of the obtained polymer 17 and the analysis / evaluation results.

(3-18) Comparative Example 2
In Example 1, the same operation as in Example 1 except that macromonomer 1 was used as a monomer component in an amount of 10 parts by mass, 40 parts by mass of MMA, 20 parts by mass of SMA, and 30 parts by mass of decyltetradecylmethacrylate (DTDMA). To obtain a base oil solution of the polymer 18 (polymer concentration 30% by mass). Table 3 shows the composition ratio of the units derived from each monomer of the obtained polymer 18 and the analysis / evaluation results.

(3-19) Comparative Example 3
In Comparative Example 2, the same operation as in Comparative Example 2 was performed except that 40 parts by mass of MMA was changed to 60 parts by mass and 30 parts by mass of DTDMA was changed to 10 parts by mass. 30% by mass) was obtained. Table 3 shows the composition ratio of the units derived from each monomer of the obtained polymer 19 and the analysis / evaluation results.

(3-20) Comparative Example 4
In Example 1, the base oil solution (polymer) of the polymer 20 was subjected to the same operation as in Example 1 except that 30 parts by mass of MMA, 30 parts by mass of SMA, and 40 parts by mass of SLMA were used as the monomer components. A concentration of 30% by mass) was obtained. Table 3 shows the composition ratio of the units derived from each monomer of the obtained polymer 20 and the analysis / evaluation results.

(3-21) Comparative Example 5
In Example 1, the same operation as in Example 1 was performed except that 12 parts by mass of macromonomer 1, 71 parts by mass of BMA, 5 parts by mass of lauryl methacrylate (LMA), and 12 parts by mass of styrene were used as the monomer components. By doing so, a base oil solution of the polymer 21 (polymer concentration 30% by mass) was obtained. Table 3 shows the composition ratio of the units derived from each monomer of the obtained polymer 21 and the analysis / evaluation results.

(4) Results Tables 2 and 3 show the composition ratio (mass basis) of the constituent units of each polymer produced in Examples and Comparative Examples, their molecular weights, and the results of physical property evaluation. The "polymer concentration at the time of measurement" of the physical property evaluation is the base oil (manufactured by SK, Inc.) so that the kinematic viscosity of the polymer at 100 ° C. is 7.0 mm ² / s when measuring the shear stability. It means the polymer concentration of the base oil solution prepared by diluting with YUBASE4).
Although the polymer used in Comparative Example 1 had a unit (B) (BMA) but did not have a unit (A) derived from a macromonomer, it was not completely dissolved in the base oil. On the other hand, the polymer used in the examples had a unit (A) derived from a macromonomer in addition to the unit (B), and therefore had excellent base oil solubility. Further, as compared with Comparative Examples 2 to 4 using a polymer having no unit (B) and having a unit derived from methyl methacrylate (MMA) introduced, the solubility in base oil and the fluidity (viscosity) near room temperature are compared. ), And the viscosity index and shear stability were excellent. The polymer used in Comparative Example 5 did not completely dissolve in the base oil because the total content of the unit (A) and the unit (B) was 83% by mass.

The viscosity index improver of the present invention can be used as a lubricating oil composition, and can be suitably used for a drive system lubricating oil, a hydraulic oil, an engine oil and the like.

Claims (8)

A polymer having a unit (A) derived from a macromonomer represented by the following formula (1) and a unit (B) derived from an alkyl (meth) acrylate and having 2 to 6 carbon atoms of the alkyl group. It is a viscosity index improver contained and

[In the formula (1), R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X ¹ represents an alkylene group, -O-, -CO-, -NH- or a linking group combining these. , The linking group contains a urethane bond, and R ² represents the polymer structural part of the macromonomer. ]
In 100 parts by mass of the polymer, the content of the unit (A) is 6 parts by mass or more and less than 20 parts by mass, the content of the unit (B) is 40 parts by mass or more and less than 74 parts by mass, and the unit (A). The total content of the unit (B) is 46 parts by mass or more and less than 80 parts by mass.
A viscosity index improver characterized in that the viscosity measured by the following method is 25 Pa · s or less.
(Viscosity measurement)
A solution consisting of 80% by mass of Group III base oil (viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² / s) and 20% by mass of the polymer in the American Petroleum Institute (API) classification is used in a viscometer (Toki Sangyo). Measured at 25 ° C with TVE-35H, 3 ° x R9.7 rotor) manufactured by the company. The unit (A) derived from the macromonomer, the unit (B) derived from the alkyl (meth) acrylate and having 2 to 6 carbon atoms of the alkyl group, and the alkyl group derived from the alkyl (meth) acrylate. A viscosity index improver containing a polymer having a unit (C) having 11 to 40 carbon atoms.
In 100 parts by mass of the polymer, the content of the unit (A) is 6 parts by mass or more and less than 20 parts by mass, the content of the unit (B) is 52 parts by mass or more and less than 74 parts by mass, and the unit (C). The content is 10 parts by mass or more and 40 parts by mass or less, and the total content of the unit (A) and the unit (B) is 60 parts by mass or more and less than 80 parts by mass.
The polymer further has a branching unit derived from a polyfunctional chain transfer agent and / or a polyfunctional polymerization initiator.
A viscosity index improver characterized in that the viscosity measured by the following method is 25 Pa · s or less.
(Viscosity measurement)
A solution consisting of 80% by mass of Group III base oil (viscosity index 122, 40 ° C. kinematic viscosity 19.6 mm ² / s) and 20% by mass of the polymer in the American Petroleum Institute (API) classification is used in a viscometer (Toki Sangyo). Measured at 25 ° C with TVE-35H, 3 ° x R9.7 rotor) manufactured by the company. The polymer is further derived from an alkyl (meth) acrylate and has a unit (C) in which the alkyl group has 11 to 40 carbon atoms.
The viscosity index improver according to claim 1, wherein the content of the unit (C) is 3 parts by mass or more and 40 parts by mass or less in 100 parts by mass of the polymer. The viscosity index improver according to claim 1 or 3 , wherein the polymer further has a branching unit derived from a polyfunctional chain transfer agent and / or a polyfunctional polymerization initiator. The viscosity index improver according to any one of claims 1 to 4 , wherein the unit (A) has a repeating structure of a branched chain alkylene group. The polymer further has a unit (D) derived from a maleimide-based monomer and has a unit (D).
The viscosity index improver according to any one of claims 1 to 5 , wherein the content of the unit (D) is 1 part by mass or more and 20 parts by mass or less in 100 parts by mass of the polymer. The viscosity index improver according to any one of claims 1 to 6 , wherein the content of the unit derived from the styrene-based monomer is less than 3 parts by mass in 100 parts by mass of the polymer. A lubricating oil composition comprising a lubricating oil base oil and the viscosity index improver according to any one of claims 1 to 7.

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